Evaluation Of In Vitro Rumen Fermentation Effects Of Medium Chain Fatty Acids On Diets With Different Concentrate To Forage Ratios

Medium chain fatty acids are fatty acids with 6～12 carbon atoms,mainly including octanoic acid（C₈）,capric acid(C₁₀)and lauric acid(C₁₂).According to previous reports,the application of medium chain fatty acids in animal production can maintain animal health,improve animal production performance and reduce methane production,but the application effect is inconsistent,which may be related to the way and level of medium chain fatty acids addition and the ratio of concentrate to roughage in diet.Therefore,in this experiment,in vitro gas production method was used to study the effects of different concentrations and types of medium chain fatty acids on rumen fermentation gas production and gas production parameters,methane production,number of rumen protozoa,fermentation parameters and in vitro dry matter digestibility of beef cattle under different concentrate to forage ratio diets,in order to provide theoretical basis for the selection of the type and amount of fatty acids and the related research.Experiment one:This experiment adopts in vitro gas method,choose the single factor experiment design,used TMR（concentrate to roughage ratio 30:70）as fermentation substrate,and in vitro rumen fluid（from Yanbian cattle）was supplemented with 1.5%（3 mg）,6%（12 mg）,9%（18 mg）and 15%（30 mg）of unesterified octanoic acid（C₈）,unesterified capric acid(C₁₀)and unesterified lauric acid(C₁₂),respectively.There were 5 treatments for each medium chain fatty acid（CON group,T1 group,T2 group,T3 group and T4 group）,3 in parallel for each treatment.The effects on gas production,gas production parameters,methane production,number of rumen protozoa,fermentation parameters,in vitro dry matter digestibility and digestive enzyme activities of beef cattle were studied.The results showed that:1)with the prolongation of fermentation time,gas production in octanoic acid group increased,but there was no significant difference among all groups（P>0.05）;The gas production of T4 group in capric acid group was significantly decreased compared with the other four groups at 48 h（P<0.05）;From 30 h in lauric acid group,gas production in groups T2,T3 and T4 was significantly decreased compared with control group and T1 group（P<0.05）.2)The production of methane and the number of rumen protozoa in octanoic acid,capric acid and lauric acid groups could be reduced to some extent.3)There were no significant differences in p H,NH₃-N concentration and lactic acid concentration between the octanoic acid and capric acid groups compared with the control group（P>0.05）,and there were no significant differences in the contents of total volatile acid,acetic acid,propionic acid and butyric acid among all groups（P>0.05）.The concentration of NH₃-N in groups T3 and T4 in lauric acid group was significantly lower than that in control group,T1 and T2 groups（P<0.05）.4)IVDMD of groups T2,T3 and T4 in capric acid group was significantly decreased compared with control group（P<0.05）;IVDMD in lauric acid group was significantly decreased compared with the control group（P<0.05）.The activities of individual digestive enzymes in octanoic acid,capric acid and lauric acid groups were increased.Based on the results of rumen liquid fermentation,9%unesterified lauric acid was the best in vitro fermentation under the condition of low concentrate diet.Experiment two:The experimental design is the same as that of Experiment one,used TMR（concentrate to roughage ratio 50:50）as fermentation substrate,the effects of different concentrations and types of medium chain fatty acids on rumen fermentation gas production,gas production parameters,methane production,rumen protozoa number,fermentation parameters,in vitro dry matter digestibility and digestive enzyme activities of beef cattle were studied.The results showed that:1)at each time point,there was no significant difference in gas production between the experimental groups of octanoic acid and the control group（P>0.05）;The gas production of T4 group in capric acid group at 30 h and 36 h was significantly decreased compared with the control group and other experimental groups（P<0.05）;From 12 h in lauric acid group,gas production in T4 group was significantly decreased compared with control group and other experimental groups（P<0.05）.2)The production of methane and the number of rumen protozoa in octanoic acid,capric acid and lauric acid groups could be reduced to some extent.3)The concentration of lactic acid in octanoic acid group T4 was significantly lower than that in T1 group（P<0.05）,but there were no significant differences in the contents of total volatile acid,acetic acid and propionic acid among all groups（P>0.05）.Compared with control group and T2 group,the concentration of lactic acid in capric acid group T3 and T4 was significantly decreased（P<0.05）,but there were no significant differences in the contents of total volatile acid and individual volatile acid among all groups（P>0.05）.Compared with the control group,the content of propionic acid in experimental groups in lauric acid group was significantly increased（P<0.05）,and the A/P in groups T3and T4 was significantly decreased compared with the control group,T1 and T2 groups（P<0.05）.4)Compared with the control group,the IVCPD of caprylic acid,caprylic acid and lauric acid groups was significantly decreased（P<0.05）;The activities of individual digestive enzymes in octanoic acid,capric acid and lauric acid groups were increased.Based on the results of rumen liquid fermentation,9%unesterified lauric acid had the best in vitro fermentation effect under medium concentrate diet.Experiment three:The experimental design is the same as that of Experiment one,used TMR（concentrate to roughage ratio 70:30）as fermentation substrate,the effects of different concentrations and types of medium chain fatty acids on rumen fermentation gas production,gas production parameters,methane production,rumen protozoa number,fermentation parameters,in vitro dry matter digestibility and digestive enzyme activities of beef cattle were studied.The results showed that:1)with the prolongation of fermentation time,gas production in octanoic acid group increased,but there was no significant difference among all groups（P>0.05）;Starting from 20 h in capric acid group,gas production in test groups was significantly decreased compared with control group（P<0.05）;At 48 h,gas production in lauric acid group was significantly lower than that in control group（P<0.05）.2)The production of methane and the number of rumen protozoa in octanoic acid,capric acid and lauric acid groups could be reduced to some extent.3)Compared with the control group,the concentration of NH₃-N in octanoic acid group was significantly decreased（P<0.05）,and there were no significant differences in the contents of total volatile acid,acetic acid,propionic acid and isobutyric acid among all groups（P>0.05）.Compared with the control group,the concentration of NH₃-N in capric acid group was significantly decreased（P<0.05）,while the A/P in capric acid group was significantly decreased（P<0.05）.The concentration of NH₃-N in lauric acid group was significantly decreased compared with the control group（P<0.05）,the content of propionic acid in lauric acid group was significantly increased compared with the control group（P<0.05）,and the A/P in lauric acid group was significantly decreased compared with the control group（P<0.05）.4)There were no significant differences in IVDMD,IVCPD,IVNDFD and IVADFD between octanoic acid,capric acid and lauric acid groups compared with control group（P>0.05）.According to the results of rumen liquid fermentation,6%unesterified capric acid and 9%unesterified lauric acid had better in vitro fermentation effect under the condition of high concentrate diet.